1. Field of the Invention
The present invention relates to an automatic focus adjusting apparatus of a camera and, more specifically, to an automatic focus detecting apparatus of a camera having a plurality of areas for focus detection.
2. Description of the Related Art
A focus adjusting apparatus employing TTL phase difference detecting method of interest to the present invention is disclosed in Japanese Patent Laying-Open Gazette No. 4914/1985. According to this article, a condenser lens and first and second image re-forming lenses are arranged behind a predetermined plane equivalent to a focal plane of a photographic lens. An amount of deviation (amount of defocus) from the predetermined focal plane of the photographic lens is detected as deviation of a distance between first and second images which are re-formed by the first and second image re-forming lenses. Automatic focus adjustment is carried out by driving the photographic lens in accordance with the result of detection. In such an automatic adjusting apparatus, photoelectric converting elements of charge accumulation type such as CCD image pick up devices are often used to detect the distance between the first and second images.
In the above described automatic focus adjusting apparatus, the lens is driven even during accumulating charges, when the lens is driven for automatic focus adjustment. However, there is a time difference between the time when charges are being accumulated by the arrangement of photoelectric converting elements and the time when the amount of driving lens is calculated based on the result of focus detecting operation in accordance with the output from the arrangement of photoelectric converting elements. Therefore, the driving amount of the lens must be corrected. Now, when there are a plurality of areas for focus detection, respective focus detecting areas corresponds to different objects, respectively. Therefore, the time for accumulating charges in the respective arrangements of photoelectric converting elements corresponding to the respective focus detecting areas are different from each other. Therefore, the lens driving amount must be corrected by different amounts in the respective arrangements of photoelectric converting elements, which correction is complicated and time consuming. In addition, memory capacitance required for the correction is large. Alternatively, if the correction of the lens driving amount for respective focus detecting areas is carried out by a prescribed correcting amount, then the resulting lens driving amount corresponds to the amount of driving the lens from different positions.